There is( 1 ) doubt that the world climate has been changing in recent years. Many people blame this change (  2)  gases such as carbon dioxide. Animals and humans produce carbon dioxide when they breathe. Many other human ( 3 ) (activity) also let off carbon gases. In order to solve this problem, one thing we can all to do is walking or

( 4 ) (use)a bicycle ( 5 )  possible. Of course, there are times when we need to travel long distance. In this case, public transport such as buses and the underground is always a ( 6 )  (good) choice than a private car or a taxi. At home you should use as little energy as possible. Turn off lights and anything else (7 )  (electricity) when not in use and its important to use( 8 ) (recycle) stuff as much as possible. Last but not least, ( 9 ) (plant) a tree every year because trees absorb the carbon dioxide in the air ( 10 ) (produce) oxygen.